In recent years, in a dialysis apparatus as a blood purification apparatus, a technology has been proposed in which priming, returning of blood and substitution (emergency fluid infusion) are performed by using a dialysate to be supplied to a dialyzer during dialysis treatment (in particular, online HDF or online HF), or a technology has been proposed in which the dialysate is used as a substitution solution for the online HDF or online HF treatment. For example, PTL 1 discloses a dialysis apparatus including a substitution line where one end is connected to a dialysate extraction port (collection port) formed in a predetermined section of a dialysate introduction line and the other end is connected to a blood circuit (arterial blood circuit or venous blood circuit): and a substitution pump which is arranged in the substitution line. In order for such a dialysis apparatus to perform the priming, the returning of blood or the substitution (emergency fluid infusion), the substitution pump is rotated to supply the dialysate in the dialysate introduction line to the blood circuit (arterial blood circuit or venous blood circuit).
In general, a cap (opening/closing device) is attachable to and detachable from the dialysate extraction port, and the substitution line is connected by detaching the cap and when the substitution line is not connected, the dialysate flowing in the dialysate introduction line is not caused to leak out by attaching the cap. For example, in order to clean and disinfect a pipe for circulating the dialysate, such as the dialysate introduction line and the dialysate discharge line, cleaning water or disinfecting solution is circulated in the pipe in a state where the cap is attached to the collection port. In this manner, the cleaning water or the disinfecting solution is prevented from leaking out. An example may be found in PTL 1: Japanese Unexamined Patent Application Publication No. 2004-313522.